Endothelium-independent relaxation and contraction of rat aorta induced by ethyl acetate extract from leaves of Morus alba (L.).
OBJECTIVE
Based on screening for vasoactive traditional Chinese medicinal herbs, the present study was performed to investigate the vasoactive effects of an ethyl acetate extract from leaves of Morus alba (L.) (ELM) on rat thoracic aorta and the mechanisms underlying these effects.


METHODS
Isolated rat thoracic rings were mounted in an organ bath system and the effects of ELM on their responses were evaluated.


RESULTS
ELM (0.125-32.000g/l) induced a concentration-dependent relaxation (P<0.01 vs. control) both in endothelium-intact and -denuded aortas precontracted by high K(+) (6 x 10(-2)M) or 10(-6)M phenylephrine (PE). In endothelium-denuded aortas, ELM at the EC(50) concentration reduced Ca(2+)-induced contraction (P<0.01 vs. control) after PE or KCl had generated a stable contraction in Ca(2+)-free solution. And after incubation with verapamil, ELM induced contraction in endothelium-denuded aortas precontracted by PE (P<0.01 vs. control); this was abolished by ruthenium red (P<0.01 vs. ELM-treated endothelium-denuded group; P>0.05 vs. control), but not by heparin (P>0.01 vs. ELM-treated endothelium-denuded group; P<0.01 vs. control).


CONCLUSIONS
The results showed that ELM had dual vasoactive effects, and the relaxation was greater than the contraction. The relaxation was mediated by inhibition of voltage- and receptor-dependent Ca(2+) channels in vascular smooth muscle cells, while the contraction occurred via activation of ryanodine receptors in the sarcoplasmic reticulum.
Xia
Manli
M
Department of Physiology, Zhejiang University School of Medicine, 388 Yuhangtang Road, Hangzhou 310058, China.
Qian
Lingbo
L
Zhou
Xinmei
X
Gao
Qin
Q
Bruce
Iain C
IC
Xia
Qiang
Q
D000085:Acetates; D000704:Analysis of Variance; D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects*; D003971:Diastole / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000502:physiology; D008297:Male; D008516:Medicine, Chinese Traditional; D031625:Morus / Q000737:chemistry*; D010936:Plant Extracts / Q000494:pharmacology*; D018515:Plant Leaves / Q000737:chemistry; D051381:Rats; D017207:Rats, Sprague-Dawley; D014661:Vasoconstriction / Q000187:drug effects*; D014664:Vasodilation / Q000187:drug effects*
D000085:Acetates; D010936:Plant Extracts; C007650:ethyl acetate